Add plugin for passing extra erl_opts flags to deps, and use it for hipe

This fixes #425 in github issue tracker

plugins/deps_erl_opts.erl

@@ -0,0 +1,12 @@
+-module(deps_erl_opts).
+-export([preprocess/2]).
+
+preprocess(Config, Dirs) ->
+    ExtraOpts = rebar_config:get(Config, deps_erl_opts, []),
+    Opts = rebar_config:get(Config, erl_opts, []),
+    NewOpts = lists:foldl(fun(Opt, Acc) when is_tuple(Opt) ->
+                                  lists:keystore(element(1, Opt), 1, Acc, Opt);
+                             (Opt, Acc) ->
+                                  [Opt | lists:delete(Opt, Acc)]
+                          end, Opts, ExtraOpts),
+    {ok, rebar_config:set(Config, erl_opts, NewOpts), []}.

rebar.config.script

@@ -157,10 +157,10 @@ CfgXrefs = lists:flatmap(
 
 ElixirConfig = case lists:keysearch(elixir, 1, Cfg) of
                    {value, {elixir, true}} ->
-                       [{plugins, [rebar_elixir_compiler, rebar_exunit] },
+                       [{plugins, [deps_erl_opts, rebar_elixir_compiler, rebar_exunit] },
                         {lib_dirs, ["deps/elixir/lib"]}];
                    _ ->
-                       []
+                       [{plugins, [deps_erl_opts]}]
                end,
 
 {ok, Cwd} = file:get_cwd(),
@@ -181,6 +181,7 @@ AllDeps = case lists:keytake(lager, 1, AllDeps0) of
 
 Config = [{erl_opts, Macros ++ HiPE ++ DebugInfo ++
                [{src_dirs, [asn1, src | SrcDirs]}]},
+          {deps_erl_opts, HiPE},
           {sub_dirs, ["rel"]},
           {keep_build_info, true},
           {ct_extra_params, "-ct_hooks cth_surefire "